RFR: 8235491: Tree/TableView: implementation of isSelected(int) violates contract

[Andy Goryachev]

…ontract

1. reword SelectionModel.isSelected(int) javadoc, removing incorrect statement "Is functionally equivalent to calling <code>getSelectedIndices().contains(index)</code>." 
2. reimplement TableView.isSelected(int) method to return true when at least one cell in *any* column is selected on the given row (was: *all* columns)
3. change selectRowWhenInSingleCellSelectionMode() and selectRowWhenInSingleCellSelectionMode2() in TableViewSelectionModelImplTest to reflect new reality.

NOTE: proposed change alters semantics of isSelected(int) method (in the right direction, in my opinion).

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Commit messages:
 - 8235491: 2022
 - 8235491: Tree/TableView: implementation of isSelected(int) violates contract

Changes: https://git.openjdk.org/jfx/pull/839/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=839&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8235491
  Stats: 46 lines in 4 files changed: 33 ins; 0 del; 13 mod
  Patch: https://git.openjdk.org/jfx/pull/839.diff
  Fetch: git fetch https://git.openjdk.org/jfx pull/839/head:pull/839

PR: https://git.openjdk.org/jfx/pull/839